This took a while to get up today because I’m kinda…Well, I got bit by a spider.
I’m allergic to spiders.
So I’m not feeling so great but I’LL BE THRICE-DAMNED IF I MISS A DAY OF THIS!
Loads and loads of extra thought, this answer did not require.

Order’s Sanctuary: the stronghold for the Warriors of Cosmos. This place is a beacon of light in a fractured world, showering the warriors with its blessed aura. The reasoning had to do with the arena’s distinct D&D!physics, and its aesthetics.
Though shown on the World Map to be a large spire surmounted with what I can only describe as a luminous, glowing chapel, Order’s Sanctuary is a large flat expanse on the inside, its floor perpetually covered with a gentle flow of water; the flat planes are broken up occasionally with slender poles, odd wave-shaped bits of terrain, and glowing rails of light. I suspect that the Sanctuary’s interior, given the positively huge expanse it covers despite having a clearly delineated border from outside, is a sort of pocket dimension.
The reason I’m so fond of this arena is acutally because of its simple beauty. It is a sculpture of wind, water, and light, simple and lovely.
There’s also a simpler reason: the fact that this is where it all begins. The start of 013…the journey’s beginning after receiving Cosmos’s benediction in 012…all simple, beautiful things that just pull you into the story from the beginning.
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Order’s Sanctuary is also a great arena for balanced fights. There are no glaring benefits or detractions for anyone here (though it does make Mateus a little bit harder to play, since there are only a few trappy corners), and even the ΩOrder’s Sanctuary is quite balanced, simply doubling your bravery on a Break.
…of course, your luck can still screw you over, as usual…
( Tell me more, tell me more! Like, is it a train? )